To fulfill the required specifications, future engine concepts call for high-speed, low-pressure turbines having high AN values, high turbine inlet temperatures and compact, short designs. To avoid hot gas ingress from the main stream, and to adjust the bearing thrust at the fixed bearing of the low-pressure system, air must be directed to the cavity between the last turbine stage and the turbine exhaust case (TEC). To optimally design this turbine disk, a thermally compensated design (avoidance of axial temperature gradients) is essential. In the case of low-pressure turbines that have been implemented in practice, this air is typically drawn off at the low-pressure compressor and routed through the low-pressure turbine shaft to the rear TEC bearing chamber. This air is used as sealing air at the bearing and for venting the rear cavity. Due to the restricted sealing air temperature (risk of oil fire, coking, etc.), the temperature of this sealing air is substantially colder than that of the cooling air which acts upon the opposite side of the rotor disk. As a result, an axial temperature gradient forms over the disk which complicates the task of providing a weight-optimized design for the rotor disk of the rotor connection. Due to the substantially inwardly drawn disk bodies required for high-speed engine concepts, and the compact design, only a very short rotor cone is possible for connection to the shaft. This reduced decay length makes the mechanical design (low-cycle fatigue lifetime) difficult. In particular, a sharp temperature gradient over the rotor cone of the shaft connection and at the corresponding disk is no longer acceptable.
The routing of the air in the case of a conventional low-pressure turbine is illustrated exemplarily in FIG. 1. Air of different temperatures acts on both sides of the cone of the rotor connection. Upstream of the shaft connection, the temperature of the rotor blade cooling air prevails; downstream of the shaft connection at the turbine exhaust case (TEC), the temperature of the bearing sealing air prevails. This results in temperature differences accompanied by high thermal stresses in the rotor cone and in the corresponding rotor disk.